mediumMultiple ChoiceObjective-mapped
AAA Authentication Login Default VTY Lines — Configuration and Troubleshooting
A network administrator is configuring AAA for device access on a Cisco router. After configuring the RADIUS server and AAA authentication login default group radius local, the engineer tests Telnet access and receives 'Access denied' even with correct credentials. The RADIUS server is reachable. What is the most likely cause?
Quick Answer
The answer is that the VTY lines are missing the login authentication default command. This is the most likely cause because the global AAA authentication login default group radius local command only defines the authentication method list; it does not automatically apply it to the VTY lines. Without explicitly binding that default list to the VTY lines using login authentication default, the router falls back to its default behavior of using the local enable password for Telnet or SSH authentication, ignoring the RADIUS server entirely. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that AAA configuration is a two-step process—defining the method list globally and then applying it to the specific lines. A common trap is assuming the global default command alone secures remote access, but the VTY lines must be explicitly told to use it. Memory tip: think of it as “global defines, VTY applies”—without the line-level command, AAA is just a ghost policy.
⚠ Common exam trap
Cisco often tests the distinction between global AAA authentication configuration and per-line application, trapping candidates who assume 'aaa authentication login default' automatically applies to all lines without the 'login authentication default' command on the VTY lines.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VTY lines are not configured with 'login authentication default'.
The 'login authentication default' command must be applied to the VTY lines to use the AAA authentication method set globally with 'aaa authentication login default group radius local'. Without this, the VTY lines default to using the local enable password for authentication, ignoring the AAA configuration. Since the RADIUS server is reachable and credentials are correct, the missing VTY line configuration is the most likely cause of the 'Access denied' error.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The VTY lines are not configured with 'login authentication default'.
Why this is correct
Correct because the AAA login method list must be explicitly applied to the VTY lines using the 'login authentication' command.
- ✗
The RADIUS server shared key is incorrect.
Why it's wrong here
Incorrect because the RADIUS server is reachable, and the issue is specific to AAA application on VTY lines.
- ✗
The enable password is not set.
Why it's wrong here
Incorrect because AAA login authentication does not require an enable password; the issue is with the method list application.
- ✗
The 'aaa new-model' command is missing.
Why it's wrong here
Without `aaa new-model`, the router does not process any AAA commands, so the `login authentication` configuration would be ignored entirely, and the device would fall back to its default local login behaviour — which in this scenario would still permit Telnet with correct credentials. The option is tempting because `aaa new-model` is a mandatory prerequisite for all AAA features; it would be the correct answer if the router were rejecting all AAA commands or showing them as unrecognised, rather than returning an explicit 'Access denied' with a reachable RADIUS server.
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
Go deeper
Related to this question
About these practice questions
One of 1,966 original 300-410 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more way this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO statements about AAA authentication on Cisco IOS-XE are true? (Choose TWO.)
hard- A.If no AAA authentication method list is explicitly configured, the default method list uses the local user database.
- ✓ B.The 'aaa authentication login default local' command creates a default method list that uses the local user database for login authentication.
- ✓ C.When a named method list is applied to a line with 'login authentication LISTNAME', the default method list is ignored for that line.
- D.The 'aaa authentication login default group radius local' command will first try RADIUS, and if RADIUS fails (not just rejects), it will fall back to local.
- E.The 'aaa authentication login default method' command creates a method list with no authentication methods, which denies all login attempts.
Why B: The 'aaa authentication login default local' command explicitly configures the default method list to use the local user database for login authentication. This is the standard way to define a fallback or primary local authentication method for all lines that do not have a named method list applied.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.